The overall objective of this research is to gain understanding of the control of antibody formation as reflected in the properties of individual antibody-forming cells. We are interested in the control of the disproportion of certain antibodies between two allotypes of globulin in rabbits heterozygotic for the principal globulin allotypes. We plan to ascertain the allotype of IgM or IgG anti-hapten globulin produced by individual cells by inhibition or enhancement with anti-allotype serums. We intend to continue our studies of the rate of formation of antibodies by individual cells in vivo. We hope that it will be possible to extend these studies to measure the formation of anti-hapten antibodies and possibly also to measure IgG antibodies and the corresponding enhanced PFC. Finally we are interested to ascertain the conditions which lead to the appearance of diverse morphology of the plaques observed in the liquid plaque assay method which we use.